It's always disappointing to see a kid come in and not reach the success that was envisioned when he signed. However, to the bolded, I think the value in that is minuscule to the value in bringing in a new kid who has a better chance at seeing the field than the one who is leaving. Is that guaranteed? No. But, having a kid on taking up a spot that isn't going to see the field, prevents the staff from having the chance of that happening.
I did a study (sorry, won't do it again) back when we had a lot of dead weight on the roster and very few left even though they weren't going to see the field. I compared that to (I think) Alabama that has lots of kids leave because, after a year or two, they know they aren't going to see the field......and then had full recruiting classes.
The number of kids going through Alabama that the staff has the chance to develop and see success with was significant compared to the number of kids that were coming through Nebraska.
To a certain extent, it's a numbers game. More kids going through the program, the better chance to find those special players.